1. Field of the Invention
The present invention relates generally to a method of manufacturing a phosphor screen for a cathode ray tube and more particularly to a method of manufacturing a phosphor layer which becomes the parent of a phosphor screen of a cathode ray tube.
2. Description of the Prior Art
As a method of manufacturing a phosphor screen for a cathode ray tube, particularly a color cathode ray tube, there has been known a so-called PVA (polyvinyl alcohol) slurry method.
According to the PVA slurry method, phosphor particles are suspended in an aqueous solution, which contains a photosensitive resin, such as ammonium bichromate or the like, a dispersing agent (surface active agent) and a binder, such as polyvinyl alcohol or the like, to thereby produce a so-called phosphor slurry. Then, the phosphor slurry is coated on the inner wall of a cathode ray tube, namely, the inner surface of its panel, which already has formed thereon a light absorption layer, for example a carbon stripe. After the phosphor slurry has been dried, it is then exposed to light by using a color selection electrode (for example, aperture grill) as an optical mask. After the exposing process, the color selection electrode is removed and the product is developed by water, thereby forming phosphor stripes of a predetermined pattern to thus form a phosphor screen on the inner surface of the panel. In general, the similar processes are sequentially repeatedly carried out to form a green phosphor stripe, a blue phosphor stripe and a red phosphor stripe. Then, the product is dried and is uniformly coated with an aqueous solution containing, for example, an acrylic resin (for example a resin sold under the trade name PRIMAL). The product is again dried to form an acrylic resin-based film, which is a so-called intermediate film on the phosphor stripes. Thereafter, a metal back layer is formed on the intermediate film by an aluminum vapor deposition process and then the whole of the product is baked to remove the intermediate film formed beneath the metal back layer. Thus, the process for manufacturing a phosphor screen is ended.
In the prior art method of manufacturing a phosphor screen for a color cathode ray tube, however, as shown in FIGS. 1A and 1B, phosphor particles 21 are crowded or overlap one another on a panel 22 so that they are brought in contact with one another in a surface contact fashion. Also, each single phosphor particle 21 has many contact portions. Thus, when the phosphor particle 21 is activated by the bombardment of electrons to emit a light, the light emitted from each phosphor particle 21 cannot pass through the phosphor particle 21 due to the existence of many contact portions of the phosphor particles 21 and, hence, the brightness of the phosphor screen cannot be demonstrated sufficiently. In FIG. 1B, reference numeral 23 designates a metal back layer.
Further, in the stage for manufacturing the phosphor screen, as shown in FIG. 2A, the phosphor particles 21 are dispersed in a displaced condition and a so-called pinhole H is formed through the phosphor particles 21 to communicate with the panel 22. The metal back layer 23, which will be formed in the later stage, enters the pinhole H and contacts with or internally touches the inner surface of the panel 22, as shown in FIG. 2B. This condition of the metal layer 23 contacting the screen at the pinhole H will cause the brightness of the phosphor screen to be considerably lowered.